Electromagnetic device



Patented June 10, 1930 UNITED STATES PATENT OFFICE NEIL Y. PRIESSMAN, OFWYOMING, NEW JERSEY, ASSIGNOR TO BELL TELEPHONE LABORATORIES,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORKELECTROMAGNETIC nEvIcn Application filed January 19, 1929. Serial No.333,644.

This invention relates to electromagnetic signaling devices, and moreparticularly to such devices wherein the force of gravity is utilized torestore the moving element or armature to its normal position.

In devices of this character it is necessary, in order to initiallyactuatethe moving element or armature from its position of rest, that aforce of sufficient ma nitude to offset the opposing force of gravity besupplied. In order to produce such a force magnetically, the core of theoperating magnet must be sufliciently energized; that is, current ofsuitable amperage must be passed through the operating winding of the manet to set up a magnetic field strong enoug to move the armature throughits operatin distance. Ordinarily, to insure the posit ve action of themoving element, a magnetizing force is employed which produces magneticsaturation of the core, so that when the magnetizing force is removed,the moving element tends to stick or adhere to the magnet core due toresidual magnetism. This sticking characteristic of devices of thisnature is objectionable.

Heretofore, this objectionable feature has been overcome or minimized toa considerable degree by the use of a comparatively heavy armature. Insuch cases the weight of the armature was made sufficiently great torender the tractive effort produced by the residual magnetismineffective, thereby insuring the prompt release of the armature uponthe cessation of the magnetizing force. The increased Weight of themoving element in this type of structure necessitates a correspondinglygreater initial tractive force to operate it, which in turn requires alarger ma netizing force for its production.

prings have also been employed in an endeavor to overcome thisobjectionable feature of sticking. The restoring force due to thesprings increases during the travel of the armature, thus obviating thenecessity for a comparatively great initial operating force. Due to thedelicate structure of such restoring springs and the precise adjustmentsrequired thereof, their use has not been entirely satisfactory.

It is the object of this invention to produce an electromagnetic devicewherein the initial force required to actuate the moving element isrelatively small and wherein a restoring force of suflicient magnitudeto overcome the sticking effect due to residual magnetism is obtained.

This object is attained in accordance with a feature of the invention bythe provision of a substantially balanced armature which is normallfulcrumed at a point approximately mi way of its extremities and which,during its actuation, is raised from its normal fulcrum and caused topivot about one of its free ends.

The invention will be readily understood from the following detaileddescription made with reference to the accompanying drawings in whichFig. 1 is a side elevation of an electromagnetic device, or dropembodying the feature of the invention; Figs. 2, 3 and 4 areconventional drawings showing several positions of the armature orshutter during the course of its actuation.

A mounting plate 5 is made of suitable dimensions to accommodate aplurality of electromagnetic signaling devices or drops, there being butone shown in the drawings. A designation strip holder 7 and a face plate6 are mounted in any suitable manner on the front face of the mountingplate 5, a spacing element 8 separating the face late 6 from themounting plate. The hol er 7 is so formed as to permit the insertion ofand retain in place the designation strip 9. A rear flange ofthemounting plate 5 is notched or slotted to accommodate the L- shapedmagnetic element 10, one end of which abuts against a metallicnon-magnetic strip 11 which extends the entire length of the mountingplate 5 and is rigidly secured thereto. The strip 11 serves as areinforcement to the Lshaped element 10 and also as a mounting for aplurality of pins 12, there being one pin for each drop. The pins 12 aresecured to the strip 11 in any suitable manner.

A J-shaped core 13 is provided with a snuglyfitting brass collar orsleeve 14 on which the wlndings 15 are mounted. The

. ter fully actuated.

when the screw 18' which. passes through the core and engages themounting block 20 is made up the core is made fast in its seat andprevented from twisting.

A shutter or armature 22' is provided with a hole substantially midwayof its ends which accommodates the pin 12. The pin is given suflicientclearance in the hole to prevent binding when the shutter is actuated.

The front end of the shutter 22 is provided with a flange whichordinaril ,has its front face colored so that when the s utter assumesits actuated position, as shown in the dashed lines in Fig. 1, thecolored face will appear before an aperture in the mounting plate andwill be readily. noticeable to the onerator, there being an aperture inthe face plate 6 in alignment with an aperture in the mounting plate.

The schematic representations shown in Figs. 2, 3 and 4 clearlyindicateseveral positions of the shutter during the course of its travelfrom normal position to its actuated position. Fig. 2 shows the shutter22 (like numerals are used in the schematics to iden' tify similar partsdisclosed in Fig. 1) 111 its:

. shown in Fig. 1. Fig. 3' discloses the shutter 22 partially actuated.It will be noted that, in this position, the shutter is about to loseits fulcrum point and to pivot about one of its ends. Fig. 4 shows theshut- In this position the shutter is raised completely from the fulcrum30. The pin 12 extending through the hole in the shutter prevents anyslippage.

In order to start the shutter in motion, a substantially smaller forceis required with the fulcrum initially midway of its extremities thanwith it at one of its free ends. This is quite obvious since thetractive. effort required initially, need only be of sufiici'entmagnitude to move the substantially balanced armature. Uponreaching aposition. such as shown in Fig. 3, the reluctance of the air-gaps isconsiderably reduced, resultingv in an increase of magnetic flux. Theforce ex erted on the armature or shutter will be correspondinglygreater and will increase as the length of the air-gap decreases.

It is evident from the foregoing that alpplicant has devised a structurein which t e large magnetizing force usually required to initiallyactuate the moving element in devices of this nature is not necessary,and the flux density in the core is reduced.

when the shutter is fully actuated, as shown; in Fig. 4, it rests on oneof its extremities so that the force of gravity acting upon the entiremass of the armature is sufficiently large to overcome the residual manetism tending to hold the shutter to the po e piece.

Applicants device permits the use of a relatively small magnetizingforce to produce sufiicient pull to positively actuate the shutter, andby changing the axis of rotation of the shutter during its motion,increases the restoring force on the shutter thereby insuring its promptrelease when the magnetiz'ing force is discontinued.

What is claimed is:

1. In an electromagnetic device, an armature having a plurality offulcrum points on which it pivots during the course of a singleactuation thereof.

2. In an electromagnetic device, an armature, a fulcrum on which saidarmature pivots during a part of its actuation, and a second fulcrum onwhich said armature pivots during another part of the same actuation.

3. In an electromagnetic device, an armature normally fulcrumed at apoint substantially midway of its ends and means for causing saidarmature to successively pivot about its normal fulcrum and one end.

4. In an electromagnetic device, an armature having a plurality ofleverages during a single actuation thereof and means for actuating saidarmature.

5. In an electromagnetic device, an energizing coil, an armature havinga plurality of' fulcrum points on which its pivots in response to theenergization of said coil.

In witness. whereof, I hereunto subscribe my name this 18th day ofJanuary, 1929.

NEIL Y. PRIESSMAN.

